From Gogeometry
Using :
- Define α = ∠BAF and β = ∠DAE
- α+β+45°=90° => α+β = 45°
- Define E’ rotation of E anticlockwise with an angle of 90°
- =>AE=AE’, β = ∠DAE = ∠BAE’
- ∠FAE’= α+β = 45°
- ΔFAE’ is congruent to ΔFAE (SAS) => FE’=FE
- Therefore a+b=x
From Gogeometry
Using :